Last modified 11/09/2005
Heath, Linda S.; Kimble, John M.; Birdsey, Richard A.; Lal, Rattan. 2003.
The Potential of U.S. Forest Soils to Sequester Carbon.
The Potential of U.S. Forest Soils to Sequester Carbon and Mitigate the Greenhouse Effect. CRC Press. Chapter 23, pp 385-394.
Previous work (Lal et al., 1998; Follett et al., 2001) described the potential of U.S. cropland and grazing land soils to sequester carbon (C) and be managed to help mitigate greenhouse-gas emissions. Activities to sequester C in croplands included land conversion, land restoration, improved cropping systems, and intensified management using conservation tillage and improved water and fertility management. Lal et al. (1998) estimated that cropland soils could sequester 75 to 208 million metric tons C per year (Mt C/year) (mean = 142), while 43 Mt C/year was estimated to be emitted from production inputs. Thus, the net potential sequestration was estimated at 100 Mt C/year on a cropland area of 136.6 million hectares (Mha) (Lal et al., 1998). Activities to sequester C in grazing lands included controlling soil erosion losses, restoring eroded and degraded soils, land conversion, and improved pasture and rangeland management, which involved fertility management, planting improved species, and grazing management. The overall potential of U.S. grazing lands to sequester C ranged from 29.5 to 110 Mt C/year (mean = 69.8) during a 25-year period, with emission losses of 12.0 to 19.5 Mt C/year (mean = 15.8 Mt C/year). The net potential sequestration of grasslands was about 53.5 Mt C/year on a land base of approximately 336 Mha. The potential to sequester C in forest soils has received little attention in the Guidelines for National Greenhouse Gas Inventories (IPCC, 1997), the Kyoto Protocol, or other studies, where the focus has been on aboveground biomass through forest-related land-use change, such as afforestation and deforestation, or forest management (Kimble et al., Chapter 1). Yet the soil in U.S. forests contains about 60% of total forest ecosystem C (Birdsey and Heath, 1995). In terms of the dynamics of C on a global basis, attempts to balance the input and output of C have revealed a "missing sink." Houghton et al. (1998) estimated this sink at 1.8 ± 1.5 Pg C/year, some of which was likely to be contained in terrestrial ecosystems in the Northern Hemisphere, namely soils and vegetation (Pacala et al., 2001). Thus, there is a need to better understand the capacity and dynamics of vegetation or forest C sinks both above and below ground. The purpose of this chapter is to synthesize key information from the present volume for easy reference. The main topics are the characteristics of forests and forest soils and how to measure and monitor them; C dynamics and soils processes, including the activity of soil organisms; forest management activities and their impacts on soils; and discussions of specific forest ecosystems with unique soil C dynamics or management needs. The typical managed forest in the conterminous United States is a productive, closed-canopy, temperate deciduous or coniferous forest. The soil C in boreal regions, high elevations, the arid West, wetlands, and subtropical areas, as well as urban areas and areas of agroforestry, may have distinct features, and so forests in these areas are treated separately. Finally, quantitative estimates of the potential of forest soils to sequester C are provided.
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